Methods of steering heavy mobile medical equipment

ABSTRACT

Methods for steering mobile medical equipment are disclosed. In one embodiment, the method includes supporting medical equipment with a base above a floor over which a left steerable wheel, a right steerable wheel, and a pair of front wheels roll; receiving an input steering angle other than zero; linearly sweeping a long link in response to the input steering angle, pivoting a pair of short links in response to the linearly sweeping of the long link; pivoting a pair of cam plates in response to the pivoting of the pair of short links; transferring the pivoting of one of the pair of cam plates to a left wheel assembly to position the left steerable wheel at a left wheel angle; and transferring the pivoting of another one of the pair of cam plates to a right wheel assembly to position the right steerable wheel at a right wheel angle.

CROSS-REFERENCE TO RELATED APPLICATIONS

This non-provisional U.S. patent application is a continuation andclaims the benefit of U.S. patent application Ser. No. 11/536,640entitled “STEERING SYSTEM FOR MOBILE MEDICAL EQUIPMENT” filed on Sep.28, 2006 by inventors Bruce M Schena and Henry Hazebrouck which isincorporated herein by reference in its entirety. U.S. patentapplication Ser. No. 11/536,640 claims the benefit of U.S. ProvisionalPatent Application No. 60/756,440 entitled “STEERING SYSTEM FOR MOBILEMEDICAL EQUIPMENT” filed on Jan. 5, 2006 by inventors Bruce M Schena andHenry Hazebrouck which is incorporated herein by reference in itsentirety.

FIELD

The embodiments of the invention relate generally to mobile carts formedical equipment. More particularly, the embodiments of the inventionrelate to steering systems for mobile robotic surgical systems.

BACKGROUND

Typical robotic surgical systems are very expensive. To make theinvestment more attractive to hospitals and surgical centers, it isdesirable to make the robotic surgical system mobile so that it can bemoved from room to room such that it is more efficiently used. Toeffectively move a mobile robotic surgical system, a steering system maybe required.

One type of steering system that may be used is an Ackerman steeringsystem that is commonly found in cars and trucks. However, the typicalAckerman steering linkage works appropriately when the turning radius isquite large. The typical Ackerman steering linkage does not work well invehicles with a small turning radius where high mobility is desirable.

It is desirable to provide a steering system for heavy medicalequipment, such as may be found in a robotic surgical system, thatoperates with a small turning radius to provide a highly mobile medicalequipment system.

BRIEF SUMMARY

The embodiments of the invention are summarized by the claims thatfollow below.

BRIEF DESCRIPTIONS OF THE DRAWINGS

FIG. 1A is a block diagram of a robotic surgery system to performminimally invasive robotic surgical procedures using one or more roboticsurgical arms.

FIG. 1B is a perspective view of the robotic patient-side system of FIG.1A with the one or more robotic surgical arms coupled thereto.

FIG. 2A is a perspective side view of a mobile base for the roboticpatient side system of FIG. 1B.

FIG. 2B is a bottom view of the mobile base illustrated in FIG. 2A.

FIG. 3 is a diagram illustrating a top view of the mobile base withlines of axes through axles of the wheels of the mobile base.

FIGS. 4A-4E are series of diagrams illustrating the desired steeringlinkage behavior for right turns of the mobile base and patient sidecart.

FIG. 5 is a diagram illustrating the desired steering linkage behaviorfor a zero radius turn of the mobile base and patient side cart.

FIG. 6 is a graph of the tiller angle TA versus the left wheel angle LWAand the right wheel angle RWA of the steerable wheels of the mobilebase.

FIG. 7 is a perspective cutaway view of the mobile base to illustratethe steering system of the patient side cart.

FIG. 8 illustrates a top cutaway view of the mobile base without thesteering tiller subassembly to better illustrate subassemblies of thesteering system of the patient side cart.

FIG. 9 illustrates a perspective side view of a steering tillersubassembly removed from the mobile base.

FIG. 10 illustrates a perspective side view of a function generatorsubassembly removed from the mobile base.

FIG. 11 illustrates a perspective side view of parallelogram linkageremoved from the mobile base.

FIG. 12 illustrates a perspective side view of a wheel assembly removedfrom the mobile base.

FIG. 13 illustrates a top view of a portion of the steering systemmounted in the mobile base of the patient side cart.

FIG. 14 illustrates a side perspective view of a short link for thesteering system of the mobile base and patient side cart.

FIG. 15 illustrates a bottom side perspective view of a portion of thesteering system mounted in the mobile base of the patient side cart.

FIG. 16 illustrates a top view of the steering system mounted in themobile base of the patient side cart.

FIGS. 17A-17C illustrate the movement of the steering system and itslinkage as it moves to steer left and right from center.

FIGS. 18A-18C illustrate schematic diagrams of the steering linkage indifferent positions.

FIG. 19 illustrates a top view of another embodiment of a steeringsystem for a patient side cart.

FIG. 20A illustrates a perspective view of the steering system of FIG.19 for a patient side cart.

FIG. 20B illustrates a magnified perspective view of a portion of thesteering system shown in FIG. 20A.

It will be appreciated that all the drawings of figures provided forherein are for illustrative purposes only and do not necessarily reflectthe actual shape, size, or dimensions of the elements being illustrated.

DETAILED DESCRIPTION

In the following detailed description of the embodiments of theinvention, numerous specific details are set forth in order to provide athorough understanding of the present invention. However, it will beobvious to one skilled in the art that the embodiments of the inventionmay be practiced without these specific details. In other instances wellknown methods, procedures, components, and circuits have not beendescribed in detail so as not to unnecessarily obscure aspects of theembodiments of the invention.

The embodiments of the invention include methods, apparatus and systemsfor a steering system for heavy mobile medical equipment.

In one embodiment of the invention, a mobile medical equipment system isdisclosed including a mobile base to movably support medical equipment,the mobile base having a chassis having a left side, a right side, afront side, and a back side; a pair of motorized wheels rotatablycoupled to the chassis near the front and the left and right sides, thepair of motorized wheels to drive the mobile medical equipment systemover a floor; a left steerable wheel and a right steerable wheelpivotally coupled to the chassis near the back side and the left sideand right side respectively, the left and right steerable wheels tosteer the mobile medical equipment system around the floor; a tillercoupled to the chassis near the back, the tiller to receive directionalinput from a user; and a steering system coupled to the chassis and theleft and right steerable wheels, the steering system including a pair ofcam followers in a pair of cam follower slots to convert directionalinput from the tiller to the left and right steerable wheels.

In another embodiment of the invention, a method for steering mobilemedical equipment having four wheels is disclosed including generating aleft wheel angle and a right wheel angle in response to an inputsteering angle other than zero, the right wheel angle differing from theleft wheel angle; transferring the left wheel angle to a left wheelassembly to position a left steerable wheel; transferring the rightwheel angle to a right wheel assembly to position a right steerablewheel; and wherein the position of the right steerable wheel differsfrom the position of the left steerable wheel, and the differentpositions of the right steerable wheel and the left steerable wheelsteer the mobile medical equipment over a floor.

In another embodiment of the invention, a steering system for mobilemedical equipment is disclosed including a left steerable wheel assemblyincluding a left steerable wheel; a right steerable wheel assemblyincluding a right steerable wheel; a left parallelogram linkage coupledto the left steerable wheel assembly, the left parallelogram linkage totransfer a left wheel angle to the left steerable wheel assembly; aright parallelogram linkage coupled to the right steerable wheelassembly, the right parallelogram linkage to transfer a right wheelangle to the right steerable wheel assembly; a steering functiongenerator coupled to the left parallelogram linkage and the rightparallelogram linkage, the steering function generator to generate theleft wheel angle (LWA) of the left steerable wheel and the right wheelangle (RWA) of the right steerable wheel; and a steering tiller coupledto the steering function generator, the steering tiller to receive aninput steering angle from an equipment operator EO to generate the leftwheel angle and the right wheel angle to control the direction of themobile medical equipment around flooring.

In another embodiment of the invention, a method for steering mobilemedical equipment having four wheels is disclosed including receiving aninput steering angle other than zero and generating a pivotal motion ina first link, converting the pivotal motion of the first link into alinear sweeping motion of a second link; converting the linear sweepingmotion of the second link into a pivotal motion of a third link and afourth link, the fourth link spaced apart from the third link; unequallytransferring the pivotal motion of the third link and the fourth linkrespectively into a first parallelogram linkage and a secondparallelogram linkage; transferring the pivotal motion in the firstparallelogram linkage to a first wheel assembly to form a first wheelangle, and transferring the pivotal motion in the second parallelogramlinkage to a second wheel assembly to form a second wheel angle, whereinthe first wheel angle differs from the second wheel angle in response tothe unequal transfer of the pivotal motion.

Robotic Surgical System

Referring now to FIG. 1A, a block diagram of a robotic surgery system100 is illustrated to perform minimally invasive robotic surgicalprocedures using one or more robotic arms with strap drive. Roboticsurgery generally involves the use of a robot manipulator that hasmultiple robotic manipulator arms. One or more of the roboticmanipulator arms often support a surgical tool which may be articulated(such as jaws, scissors, graspers, needle holders, micro dissectors,staple appliers, tackers, suction/irrigation tools, clip appliers, orthe like) or non-articulated (such as cutting blades, cautery probes,irrigators, catheters, suction orifices, or the like). At least one ofthe robotic manipulator arms (e.g., the center robotic manipulator arm158B) is used to support a stereo or three dimensional surgical imagecapture device 110 such as a stereo endoscope (which may be any of avariety of structures such as a stereo laparoscope, arthroscope,hysteroscope, or the like), or, optionally, some other stereo imagingmodality (such as ultrasound, fluoroscopy, magnetic resonance imaging,or the like). Robotic surgery may be used to perform a wide variety ofsurgical procedures, including but not limited to open surgery,neurosurgical procedures (such as stereotaxy), endoscopic procedures(such as laparoscopy, arthroscopy, thoracoscopy), and the like.

A user or operator O (generally a surgeon) performs a minimally invasivesurgical procedure on patient P by manipulating control input devices160 at a master control console 150. A computer 151 of the console 150directs movement of robotically controlled endoscopic surgicalinstruments 101A-101C by means of one or more control cables 159,effecting movement of the instruments using a robotic patient-sidesurgery system 152 that is also referred to as a patient-side cart(PSC). The robotic patient-side surgery system 152 has one or morerobotic arms 158. In a preferred embodiment of the invention, the one ormore robotic arms 158 have a strap drive system. Typically, the roboticpatient-side surgery system 152 includes at least three roboticmanipulator arms 158A-158C supported by linkages 156, 156′, with acentral robotic arm 158B supporting an endoscopic camera 101B and therobotic arms 158A, 158C to left and right of center supporting tissuemanipulation tools 101A and 101C.

Generally, the robotic patient-side surgery system 152 includes apositioning portion and a driven portion. The positioning portion of therobotic patient-side surgery system 152 remains in a fixed configurationduring surgery while manipulating tissue. The driven portion of therobotic patient-side surgery system 152 is actively articulated underthe direction of the operator O generating control signals at thesurgeon's console 150 during surgery. The actively driven portion of therobotic patient-side system surgery 152 is generally referred to hereinas the robotic arms or alternatively to robotic surgical manipulators.The positioning portion of the robotic patient-side surgery system 152that is in a fixed configuration during surgery may be referred to as“set up arms” 156, 156′ with positioning linkage and/or “set-up joints”(SUJ). In an alternate embodiment of the invention, the roboticpatient-side surgery system 152 may be replaced by set up arms thatcouple at one end to left and right sides of the operating table T. Thethree robotic manipulator arms 158A-158C may then be coupled to theopposite end of the set-up arms to ground to the table T.

For convenience in terminology, manipulators such as robotic surgicalarms 158A and 158C actuating the tissue affecting surgical tools 101Aand 101C are generally referred to herein as a PSM (patient-sidemanipulators), and a robotic surgical arm 158B controlling an imagecapture or data acquisition device, such as the endoscopic camera 101B,is generally referred to herein as a ECM (endoscope-camera manipulator),it being noted that such telesurgical robotic manipulators mayoptionally actuate, maneuver and control a wide variety of instruments,tools and devices useful in surgery. The surgical tools 101A, 101C andendoscopic camera 101B may be generally referred to herein as tools orinstruments 101.

An assistant A may assist in pre-positioning of the robotic patient-sidesurgery system 152 relative to patient P as well as swapping tools orinstruments 101 for alternative tool structures and the like, whileviewing the internal surgical site via an assistant's display 154. Withthe embodiments of the invention, the assistant A may also swap in andout the robotic surgical arms 158A and 158C, as well as the roboticsurgical arm 158B, in case one is defective or failing. In other cases,a robotic surgical arm may be swapped out for maintenance, adjustments,or cleaning and then swapped back in by one or more service persons.

Referring now to FIG. 1B, a perspective view of the robotic patient-sidesystem 152 is illustrated. The robotic patient-side surgery system 152may have one or more robotic surgical arms (a.k.a., robotic surgicalmanipulators) 158A-158C with a strap drive system to manipulate the armand any robotic surgical tool coupled there-to. The robotic arms 158A,158C are for coupling to robotic surgical tools 101A, 101C. The roboticarm 158B is for coupling to an endoscopic camera 101B. Generally, thesurgical robotic arms 158A-158C may be referred to as a surgical roboticarm or a robotic surgical arm 158.

The robotic patient-side surgery system 152 further includes a mobilebase 200 from which the robotic surgical instruments 101 may besupported. More specifically, the robotic surgical instruments 101 areeach supported by the positioning linkage 156 and the surgical roboticarms 158. The linkage structures may optionally be covered by protectivecovers or not to minimize the inertia that is manipulated by theservomechanism and the overall weight of robotic patient-side surgerysystem 152.

The robotic patient-side surgery system 152, an exemplary mobile medicalequipment system, is designed to be rolled around the hospital corridorsand within the operating room. The robotic patient-side surgery system152 generally has dimensions suitable for transporting between operatingrooms. It typically can fit through standard operating room doors andonto standard hospital elevators. The robotic patient-side surgerysystem 152 may have a weight and a wheel (or other transportation)system that allows the cart to be positioned adjacent to an operatingtable by a single attendant. The robotic patient-side surgery system 152may be sufficiently stable during transport to avoid tipping and toeasily withstand overturning moments that may be imposed at the ends ofthe robotic arms during use. The robotic patient-side surgery system 152weighs approximately one-thousand two-hundred pounds in one embodimentof the invention. The robotic patient-side surgery system 152, includingthe robotic arms 158, set up arms, and the mobile base 200, is alsoreferred to herein as the “Patient Side Cart” or PSC 152.

Mobile Base

Referring now to FIG. 2A, a perspective side view of the mobile base 200is illustrated without any robotic arms or any set up arms coupledthere-to in order to better illustrate the elements of the base 200.However, the robotic patient-side surgery system 152 typically includesthe setup arms 156, the set up joints 156′, and a plurality of roboticsurgical arms 158A,158B,158C.

The mobile base 200 includes a tiller 202 to steer and move the roboticpatient-side surgery system 152 around hospital corridors and operatingrooms. The tiller 202 may alternatively be referred to as a steeringwheel. The mobile base 200 further includes a column 201 to which a setup arm can moveably couple to support a robotic surgical arm 158 over apatient. FIG. 1B illustrates the column 201 supporting a plurality ofrobotic surgical arms 158A, 158B, 158C by way of the setup arms 156 andset up joints 156′. It is to be understood that a reference to themobile base 200 herein is also a reference to the robotic patient-sidesurgery system 152 including the set up arms and set up joints.

Referring now to FIG. 2B, the mobile base 200 of the roboticpatient-side surgery system 152 further has four wheels204R,204L,205R,205L. In order to maximize mobility of the PSC 152 in thevicinity of an operating room table, a “front-wheel-drive,rear-wheel-steer” (e.g. forklift-like) system was chosen. The two frontwheels 204R,204L may be motorized wheels and in a fixed orientationrelative to the mobile base 200 in one embodiment of the invention. Inanother embodiment of the invention, the two front wheels 204R,204L arerotatably coupled to the chassis in a fixed orientation relative to themobile base 200 but are not motorized. In either case, the two frontwheels 204R,204L are non-steerable and can roll the mobile base over afloor.

The two rear wheels 205R,205L are non-motorized but are steerable wheelsthat can be steered by the tiller 202 to turn the mobile base 200.

This front-wheel-drive, rear-wheel-steer” (e.g. forklift-like) systemprovides significant design advantages as well—the motorized wheels204R,204L are nicely packaged in the front “pontoons” 207R,207L whilemore space could be provided toward the rear of the mobile base 200 forthe steering mechanism and “swing room” for the two rear wheels205R,205L and their respective steerable wheel assemblies.

The mobile base 200 further has a cast chassis 210 to support therobotic patient-side surgery system 152 on the motorized wheels204R,204L and the two rear steerable wheels 205R,205L. The cast chassis210 receives the motorized wheel assemblies and the steerable wheelassemblies for the wheels 204R,204L and 205R,205L, respectively. Themobile base 200 further has enclosure covers 212A,212B to cover over themotorized wheel assemblies and the steerable wheel assemblies coupled tothe chassis 210.

Each of the motorized wheel assemblies includes a motorized wheel204L,204R, a motor 212, and a chain drive 214 coupled together andmounted in a pontoon 207L,207R of the chassis 210. Each of the motors212 in the pontoons 207L,207R are controlled by a variable speed controlswitch 215 that is readily accessible to a user near the handles 217 ofthe tiller 202.

Referring now to FIG. 3, a top view of the mobile base 200 with lines ofaxes 301-303 drawn through wheel axles to a center of turn 305. Line ofaxis 301 represents the fixed front wheel axis around which themotorized wheels 204L,204R rotate. That is, the motorized wheels204L,204R are perpendicular to the axis 301. Line of axis 302 representsthe steerable left wheel axis around which the left rear steerable wheel205L rotates. That is, the left rear steerable wheel 205L isperpendicular to the axis 302. Line of axis 303 represents the steerableright wheel axis around which the right rear steerable wheel 205Rrotates. That is, the right rear steerable wheel 205R is perpendicularto the axis 303. As illustrated in FIG. 3, lines 301-303 substantiallyintersect at the center of turn 305 about which the mobile base 200 canrotate. The center of turn 305 may also be referred to herein as acenter of turning, a center turn point or an instant center. Note thatthe axes 301-303 may not perfectly intersect at the center of turn 305due to compromises/tradeoffs made in the design of the steering systemas well as due to manufacturing imperfections in the components and wearin the steering system as it is used over time.

FIG. 3 illustrates how the basic principles of Ackerman steering areapplied to the robotic patient-side surgery system 152. A keyrequirement of any good steering system for a four-wheel vehicle is thatthe axis 301-303 defined by the rotation of each wheel (e.g. axle)should substantially intersect (ideally) at a single center turn point305 (also referred to as the “center of turn”, “center of turning” or“instant center”). Since the front wheels 204L,204R of the PSC 152 arefixed (e.g. non-steerable), the axes 302-303 drawn from each of the two(rear) steerable wheels 205L,205R substantially intersect near the samepoint somewhere along the fixed, front-wheel axis 301. While an AckermanLinkage works well with in cars and trucks where the turning radius isquite large, it does not work well for high mobility, small turningradius vehicles.

As illustrated in FIGS. 2A-2B and 3, an equipment operator EO operatesthe mobile base 200 at its rear by turning the tiller 202 to move thesteering mechanism that rotates the two (rear) steerable wheels205L,205R. The operator EO further controls the forward and rearwardmotion of the mobile base 200 by the variable speed control switch 215controlling the power supplied from the rechargeable batteries 220 toeach motor 212 driving the motorized wheels 204L,204R.

Referring now to FIGS. 4A-4E, a series of diagrams illustrate thedesired steering linkage behavior for right turns of the mobile base 200and PSC 152. The desired steering linkage behavior for left turns of themobile base 200 and PSC 152 are simply mirror images of FIGS. 4B-4E.FIG. 8 illustrates one diagram of the position of the steering linkagefor a left turn of the mobile base 200 and PSC 152.

In FIG. 4A, the PSC 152 is moving straight forward. The steerable wheels205L,205R are pointed straight and parallel to each other (steerablewheels 205L,205R are “centered”) to move the mobile base 200 straightforward. As a result, the axes 302,303 substantially intersect the axis301 at infinity so that the mobile base 200 has an infinite turningradius.

In FIG. 4B, the PSC 152 is executing a large-radius sweeping turn. Thesteerable wheels 205L,205R are pointed slightly to the left so that theaxes 301, 302B, 303B substantially intersect a long distance away fromthe mobile base 200 at the center turn point 305B.

In FIG. 4C, the PSC 152 is executing a medium radius turn. The steerablewheels 205L,205R are pointed to the left so that the axes 301, 302C,303C substantially intersect at the center turn point 305C.

In FIG. 4D, the PSC 152 is executing a tight radius turn. The steerablewheels 205L,205R are pointed to the left so that the axes 301, 302D,303D substantially intersect at the center turn point 305D.

In FIG. 4E, the PSC 152 is executing a very tight radius turn. Thesteerable wheels 205L,205R are pointed more sharply to the left so thatthe axes 301, 302E, 303E substantially intersect just at the outer edgeof the PSC 152 at the center turn point 305E.

In the series of FIGS. 4A-4E, it can be observed that the center turnpoint 305 moves from infinity (FIG. 4A) to near the PSC 152 at point305E as the wheels are turned toward the left away from center. Thecenter turn point would similarly move from infinity to near the PSC 152as the steerable wheels 205L,205R are turned toward the right away fromcenter.

Referring momentarily to FIG. 8, the steering linkage and steerablewheels are positioned to execute a left turn. The steerable wheels205L,205R are pointed to the right so that the axes 301, 302G, 303Gsubstantially intersect at the left center turn point 305G.

In the series of FIGS. 4A-4E and 8, the steerable wheels 205L,205R arepointed in the same direction. However, in one embodiment of theinvention, the steerable wheels 205L,205R can be controlled by thetiller 202 so that they point in different directions.

In FIG. 5, the PSC 152 is executing a “Zero Radius” turn. The steerablewheels 205L,205R are pointed in different directions so that the axes301, 302F, 303F substantially intersect within the PSC 152 at the centerturn point 305F. The “zero radius turn” is a special case where the PSC152 turns around a point 305F directly between the “pontoons” 207L,207Rof the mobile base 200. Depending upon which direction the tiller 202 isturned, the motor 212 for motorized wheel 205L is controlled in onedirection while the motor 212 for the motorized wheel 205R is controlledto move in the opposite direction to execute the zero radius turn.

While a zero radius turn can be accomplished by the embodiments of thesteering linkage disclosed herein, it has been mechanically prevented ina number of embodiments of the invention to avoid the complex motorcontrol required to drive the motorized wheel 205L in one directionwhile driving the motorized wheel 205R in the opposite direction.Instead, the smallest radius turn has been limited to have a radius ofapproximately equal to half the width of the PSC 152.

The use of the four wheels 204L,204R,205L,205R greatly increases thestability of the PSC 152 over that of tri-pod wheel systems whilemaintaining the maneuverability and the intuitive steering found inthree-wheel designs.

While a mechanical steering linkage may be used to steer the mobile base200, the steering may also be electronically controlled in an alternateembodiment of the invention. In this case, the tiller may generate anelectronic signal representing a tiller angle that is processed togenerate a left wheel angle and a right wheel angle that is respectivelytransferred to a left electrical motor and a right electrical motor torespectively turn a left steerable wheel and a right steerable wheeldirectly or through a drive train or mechanical linkage.

Steering Mechanism

For a particular cart configuration (wheelbase, distance between frontwheels, distance between back wheels, etc) the left and right steeringangles can be computed which provide the “ideal Ackerman” steeringsystem geometry.

FIG. 6 illustrates a graph showing the tiller angle TA (steering input)versus the left wheel angles (LWA) and the right wheel angles (RWA) toprovide the proper steering behavior for an exemplary mobile base 200having a wheelbase of thirty-four inches and a front and rear wheelseparation (track width) of twenty-three inches in one embodiment of theinvention.

When the tiller is positioned at center having a tiller angle (TA) ofzero degrees, as is illustrated in FIG. 4A, a left wheel angle (LWA) ofthe left steerable wheel 205L and a right wheel angle (RWA) of the rightsteerable wheel 205R are also substantially zero degrees. However, whenthe tiller is moved away from center so that the TA is not zero degrees,the right wheel angle and the left wheel angle change from zero but atdifferent rates. That is, for a given TA greater than or less than zero,the RWA and the LWA are not equal.

In one embodiment of the invention, the tiller 202 moves over the rangeof tiller angles from positive ninety degrees to negative ninetydegrees. In another embodiment of the invention, the tiller 202 movesover the range of tiller angles from positive seventy degrees tonegative seventy degrees.

Referring now to FIG. 7, a perspective cutaway view of the mobile base200 is illustrated. The steering system 700 of the mobile base 200 andPSC 152 consists of four major subassemblies.

The first subassembly of the steering system 700 of the mobile base 200is a steering tiller subassembly 900. The steering tiller subassembly900 includes the tiller 202 with handlebars which an equipment operatorEO uses to steer the PSC. The steering tiller subassembly 900 receivesthe input steering angle (also referred to as the tiller angle TA) fromthe operator EO. The steering tiller subassembly 900 is betterillustrated in FIG. 9.

The second subassembly of the steering system 700 of the mobile base 200is a steering function generator 1000. The steering function generator1000 is a slot/cam/parallelogram mechanism which generates the properwheel angles (LWA and RWA) as a function of the input steering angle(also referred to as the tiller angle TA). The steering functiongenerator 1000 is better illustrated by FIG. 10.

The third subassembly of the steering system 700 of the mobile base 200is a pair of -four-bar, Sine/Cosine parallelogram linkages 1100L, 1100R.Each side of the four-bar, Sine/Cosine parallelogram linkages transfersthe “wheel angles” from the cam mechanism to the left and right wheelassemblies 1200L, 1200R. The right side four-bar, Sine/Cosineparallelogram linkage 1100R is better illustrated by FIG. 11. With acentered tiller at a tiller angle (TA) of zero degrees the assembly ofthe components of the steering system is symmetric about a centerline ofthe PSC 152 such that the left side four-bar, Sine/Cosine parallelogramlinkage is a mirror image of the right side.

The fourth subassembly of the steering system 700 of the mobile base 200is the pair of steerable wheel assemblies 1200L,1200R. The positions ofthe steerable wheels in the steerable wheel assemblies 1200L, 1200Rcontrol the direction of the mobile base around flooring. A steerablewheel assembly 1200 for each of the pair of steerable wheel assemblies1200L, 1200R is better illustrated by FIG. 12.

Referring now to FIG. 8, a top cutaway view of the mobile base 200 isillustrated without the steering tiller subassembly. FIG. 8 illustratesthe steering function generator 1000 coupled to the left and rightfour-bar, Sine/Cosine Parallelogram linkage 1100L, 1100R. FIG. 8 furtherillustrates the left and right four-bar, Sine/Cosine Parallelogramlinkage 1100L, 1100R coupled to respective left and right steerablewheel assemblies 1200L,1200R.

FIG. 8 also illustrates a top view of the left and right motorized wheelassemblies 1200L, 1200R including the motorized wheels 204L,204R. Eachassembly includes a sprocket 804 to couple to the drive train 214 thatis driven by the motor 212 (see FIG. 2B). The sprocket 804 is furthercoupled to a rim of the motorized wheel to drive the wheel. A chain,belt, and/or one or more additional gears in the drive train 214 couplesthe sprocket 804 to the electric motor 212. Each assembly furtherincludes a first bearing 807 and a second bearing 806 rotatably couplinga shaft of motorized wheel 204L,204R to the chassis 210 of the mobilebase 200.

Referring now to FIG. 9, a perspective side view of the steering tillersubassembly 900 removed from the mobile base 200 is illustrated. Asdiscussed previously, the steering tiller subassembly 900 receives theinput steering angle (also referred to as the tiller angle TA) from anequipment operator EO that turns the tiller 202.

The steering tiller subassembly 900 includes the tiller 202 having atiller shaft 904 and handlebars 217 coupled to the shaft at one end asillustrate in FIG. 9. An equipment operator EO uses the handlebars torotate the shaft 904 to steer the PSC 152. The steering tillersubassembly 900 further includes a pinion gear 908 coupled to the shaft904 of the tiller 202 near an end opposite the handlebars 217. Thesteering tiller subassembly 900 further includes a pair of spaced apartbearings 906 which are coupled to the shaft 904 between the gear 908 andthe handlebars 217. The pair of bearings 906 rotatably couple the tiller202 to the chassis 210 of the mobile base 200.

Referring now to FIG. 10, a perspective side view of the functiongenerator subassembly 1000 removed from the mobile base 200 isillustrated. As discussed previously, the steering function generator1000 generates the proper wheel angles (LWA and RWA) as a function ofthe input steering angle (also referred to as the tiller angle TA)received from the steering tiller subassembly 900.

The steering function generator 1000 is a slot/cam/parallelogrammechanism including a tiller link 1001; a long link 1002 (may alsoreferred to as a sliding bar); left and right short links 1004L,1004R(may also referred to as ground links); and left and right cam plates1006L,1006R with each having an angled arm and a cam follower slot. Thetwo short links 1004-1004R, the tiller link 1001, and the long link1002, along with ground of the chassis 210, form a parallelogramstructure 1050.

The tiller link 1001 is pivotally coupled to the chassis 210 of themobile cart 200 near one end by a pivotal shaft 1012. Near an oppositeend, the tiller link 1001 is pivotally coupled to the long link 1002 bya pivotal shaft 1013. The pivotal shaft 1012 is coupled to the chassis210. The pivotal shaft 1013 is coupled to the long link 1002. Bearings1015 in the tiller link 1001 around the pivotal shafts 1012-1013 allowthe tiller link 1001 to pivot about each.

The tiller link 1001 includes an opening or slot 1011 through which thetiller 202 and pinion gear 908 are inserted. An internal sector gear1010, an arctuate gear segment, is rigidly coupled to the tiller link1001 by bolts (not shown in FIG. 10). The internal sector gear 1010meshes with the pinion gear 908 of the tiller 202 to receive therotation of the tiller 202. In this manner, the tiller link 1001 andsteering function generator 1000 receive the rotation of the tiller 202that represents the tiller angle TA. Note that the tiller 202 may coupleto the tiller link 1001 in other ways such as through a belt and pulleysystem, a chain and gear system, or a direct-drive.

The angular rotation of the tiller 202 causes the tiller link 1001 topivot at one end about the pivotal shaft 1012 coupled to the chassis210. The pivotal movement in the tiller link 1001 is linearly coupled tothe long link 1002 through the pivotal shaft 1013. That is, the tillerlink 1001 substantially converts the angular rotation of the tiller 202into a lateral sweeping motion of the long link 1001.

The long link 1002 pivotally couples to the left short link 1004Lthrough a pivotal shaft 1020L near one end and to the right short link1004R through a pivotal shaft 1020R near an opposite end. The pivotalshaft 1020L is coupled to the left short link 1004L. The pivotal shaft1020R is coupled to the right short link 1004R. Bearings in the longlink 1002 around the pivotal shafts 1020L-1020R allow the long link 1002and the short links 1004L-1004R to pivot respectively about each otherthere-at. In one embodiment of the invention, the bearings around thepivotal shafts are needle bearings but could also be roller bearings orother types of ball bearings.

The long link 1002 converts its lateral sweeping motion (may alsoreferred to as a linear sweeping motion) into pivotal motion of each ofthe short links 1004L-1005R. In essence, the pivotal motion of thetiller link 1001 is coupled into pivotal motion in each of the shortlinks 1004L, 1004R by the long link 1002.

As illustrated in FIG. 10, the left and right short links 1004L,1004Reach include a cam follower 1042 (see also FIG. 14) near a first endthat is inserted into cam follower slots 1060L,1060R in each of the leftand right cam plates 1006L,1006R, respectively. Also near the first endof each of the short links 1004L,1004R, the short links 1004L,1004R arepivotally coupled by pivotal shafts 1020L,1020R to the long link 1002near its opposite ends. The pivotal shafts 1020L, 1020R are coupled tothe short links 1004L,1004R, respectively. Near the second end of theleft and right short links 1004L, 1004R opposite the first end, each ofthe left and right short links 1004L,1004R are pivotally coupled to thechassis 210 by pivotal shafts 1041. The pivotal shafts 1041 are coupledto the chassis 210. Bearings in the left and right short links 1004L,1004R around the pivotal shafts 1041 allow the short links to pivot atthe axis of the pivotal shafts 1041. Bearings in the long link 1001around the pivotal shafts 1020L, 1020R allow the short links to pivot atthe axis of the pivotal shafts 1020L,1020R.

As discussed previously, a cam follower 1042 of each short link1004L,1004R is inserted into cam follower slots 1060L,1006R in eachrespectively cam plate 1006L, 1006R. The pivotal motion of the shortlinks 1004L,1004R is converted into a rotational or pivotal motion ofvarying degrees in the cam plates 1006L,1006R about pivotal shafts 1061by the cam follower and cam follower slots. In one embodiment of theinvention, the cam follower slots 1060L, 1060R are linear in shape toprovide a linear cam profile. In other embodiments of the invention, thecam follower slots may be curved to provide a curved cam profile or havea complex shape to provide a complex cam profile. Note that the camslots should be slightly wider than the maximum diameter of the camfollower. That is, the diameter of the cam followers 1042 should be lessthan the width of the cam follower slots 1060L,1060R so that there maybe a small gap to one side. This is to prevent “scrubbing” (rubbing onboth sides simultaneously) of the cam followers in the cam followerslots. The larger width of the cam slots over the diameter of the camfollower slots contributes a small amount of backlash, but reduces wearand friction in the steering system.

As shown in FIGS. 10, 11, 13, and 15, the cam plates 1006L,1006R have apair of angled arms forming a letter-V-like shape that pivot about thepivotal shafts 1061 near a base. As shown in FIGS. 10, 11, 13, and 15, acam follower slot 1060L,1060R,1060 is formed along a portion of theangled arm of each cam plate 1006L,1006R,1006. The cam plates1006L,1006R are mirror images of each other. However, the cam plates1006L,1006R are pivotally mounted with their angled arms forming theletter-V-like shapes pointing outward towards the respective left andright wheel assemblies with their pivot points oriented toward thecenter of the cart. The cam plates 1006L,1006R provide varying anddifferent degrees of wheel angle (LWA,RWA) in the left and rightsteerable wheels, such as illustrated in FIG. 6.

Inserted in each of the cam plates 1006L,1006R are bearings around thepivotal shafts 1061 to allow them to pivot around the axis there-at. Thepivotal shafts 1061 are coupled to a pair of pivot plates (see pivotplates 1606L,1606L in FIG. 16) that are coupled to the chassis 210. Inthis manner, the cam plates 1006L, 1006R are pivotally coupled to thechassis 210. Near the tops of the letter-V-like shape, each angled armof the cam plates 1006L, 1006R pivotally couple to a pair of steeringlinks (that may also referred to as tie rods) of the parallelogramlinkage 1100L,1100R through the pivotal shafts 1066-1067 (see FIG. 11).As shown in FIG. 11, the respective cam plates 1006 are coupled to therespective left and right wheel assemblies through the parallelogramlinkage 1100 to steer the steerable wheels.

Referring now to FIG. 11, a perspective side view of one parallelogramlinkage 1100 removed from the mobile base 200 is illustrated. Theparallelogram linkage 1100 that is illustrated in FIG. 11 is the rightside parallelogram linkage 1100R. When the tiller is centered with atiller angle of zero degrees the steering system is symmetric about acenter line such that the left side parallelogram linkage 1100L is amirror image of the right side parallelogram linkage 1100R havingsubstantially similar components.

The parallelogram linkage 1100 includes the cam plate 1006, a rearsteering link 1102R, a front steering link 1102F, and a caster link 1104pivotally coupled together at the pivotal shafts 1066,1067,1106,1107 asillustrated in FIG. 11. Through the pivotal shafts 1067 and 1107, theends of the rear steering link 1102R are pivotally coupled to the camplate 1006 and the caster link 1104 near a first end of each. Throughthe pivotal shafts 1066 and 1106, the ends of the front steering link1102F are pivotally coupled to the cam plate 1006 and the caster link1104 near a second end of each opposite their first ends.

The caster link 1104 is coupled to a caster bracket 1202 to steer one ofthe steerable wheels.

Referring momentarily to FIG. 12, each caster bracket 1202 of each wheelassembly 1200 is pivotally coupled to the chassis 210 by one or morebearings 1204 through the pivotal shaft 1206. The pivotal shaft 1206 isrigidly coupled to the caster bracket 1202 so that they pivot togetheras a pivoting assembly. The caster bracket 1202 and the wheel assembly1200 pivot about the axis 1210 through the pivotal shaft 1206 asillustrated in FIGS. 11 and 12.

Referring now back to FIG. 11, the rotational motion of the cam plate1006 is converted into equal but opposite lateral sweeping motion in therear steering link 1102R and the front steering link 1102F. As the rearsteering link 1102R is pushed laterally by the cam plate 1006, the frontsteering link 1102F is laterally pulled on by the cam plate.Accordingly, the rear steering link 1102R pushes on the first end of thecaster link 1104 and the front steering link 1102F pulls on the secondend of the caster link 1104. In response, the caster link 1104 pivots inone direction around the axis 1210. Conversely, as the front steeringlink 1102F is laterally pushed by the cam plate, the rear steering link1102R is laterally pulled on by the cam plate. Accordingly, the rearsteering link 1102R pulls on the first end of the caster link 1104 andthe front steering link 1102F pushes on the second end of the casterlink 1104. In response, the caster link 1104 pivots in an oppositedirection around the axis 1210. In this manner, the rotational orpivotal motion of the cam plate 1006 is transferred out to the casterlink 1104 by the parallelogram linkage 1100.

Between the left parallelogram linkage 1100L and the right parallelogramlinkage 1100R, the distance of lateral movement in the rear steeringlink 1102R and the front steering link 11102F differs so that the LWAand the RWA differ, such as illustrated in FIG. 6 for example.

Referring now to FIG. 12, a perspective side view of the wheel assembly1200 removed from the mobile base 200 is illustrated. The wheel assembly1200 includes the steerable wheel 205L,205R, an axle 1201, bearings1208, the caster bracket 1202, bearings 1204, and pivotal shaft 1206.The steerable wheel 205L,205R is rotatably coupled to the caster bracket1202 by the axle 1201 and the bearings 1204. The axle 1201 of thesteerable wheel 205L,205R is substantially concentric to the axis302,303. Thus, each steerable wheel 205L,205R rotates about its axle1201 and its respective axis 302,303.

As discussed previously, the caster link 1104 is coupled to the casterbracket 1202 to steer the steerable wheel 205L,205R. Thus, the pivotalmotion of the caster link 1104 is coupled to the caster bracket 202 andthe steerable wheel 205L,205R. The caster link 1104, the caster bracket1202, and the wheel assembly 1200 pivot about the axis 1210 through thepivotal shaft 1206 in response to the linear movement in the rearsteering link 1102R and the front steering link 1102F. That is, thepivotal motion of the cam plate 1006L,1006R is couple into pivotalmotion of the wheel assembly 1200 through the parallelogram linkage1100. Note that another wheel may be included in the wheel assembly 1200to form a double wheeled assembly for greater load carrying capability.

The wheel contact patch of each steerable wheel 205L,205R does not haveto be located directly below the axis 1210 of rotation of the wheelassembly 1200. In this case, the wheel contact patch is slightly offset(such as approximately three-fourths of an inch for example) from theaxis 302,303 of rotation of the center of the wheel. The wheel should tobe sufficiently offset so that the actual contact patch of thetire/wheel is offset to one side of the center axis 302,303 of rotation.

The offset in the wheel contact patch keeps the wheel from “scrubbing”on the floor (marking, wear) and instead enables the wheel to rollaround the axis of rotation with less resistance to the equipmentoperator EO moving the tiller. Otherwise, if the wheels were centered sothat the contact patch was in line with the axis 1201 over the centeraxis 302,303, the scrubbing of the on-axis contact patch can generatehigh resistance that is felt by the operator EO. Various amounts ofscrubbing can occur if the center of rotation 302,303 is inside of thecontact patch with the flooring.

Operation

Reference is now made to FIG. 13 illustrating a top view of a portion ofthe function generator 1000. FIG. 13 better illustrates the cam plate1006L,1006R and their respective cam follower slots 1060L,1060R. FIG. 13illustrates the pivot bearing 1361 in the cam plate 1006L to pivot thecam plate about the pivotal shaft 1061.

In operation, an equipment operator EO holds the tiller handles 217 toturn the tiller 202 and steer the PSC 152. The tiller 202 rotatesapproximately ±70° from the straight-ahead or centered position. Thetiller handles 217 turn the tiller shaft 904 and the pinion gear 908coupled near its end. In one embodiment of the invention, the piniongear 908 has twenty-three teeth. The pinion gear 908 meshes with aninternal sector gear 1010, an arctuate gear segment. If the internalsector gear 1010 were completely fully circular, it would have eightyteeth in one embodiment of the invention. Thus, the gear ratio betweenthe internal sector gear 1010 and the pinion gear 908 is eighty overtwenty-three or 3.478 to 1.

The internal sector gear 1010 is attached to the tiller link 1001. Thetiller shaft 904 passes through a slot 1011 in the tiller link 1001. Theslot 1011 restricts the angular motion of the tiller link 1001 to plusand minus twenty degrees around the pivot axis 1303. In FIG. 13, thetiller link 1001 is shown at approximately eleven degrees clockwise fromits centered position.

As discuss previously, the two short links 1004L,1004R, the tiller link1001, and the long link 1002, in addition to ground, form a pivotableparallelogram structure 1050. Pivot axes 1301, 1302, and 1303 of thepivotable parallelogram structure are grounded. As the tiller link 1001is driven back and forth by the tiller shaft pinion gear 908, the twoshort links 1004L, 1004R move in a substantially similar way.

Note that pivotable parallelogram mechanism 1050 is technically overconstrained due to the presence of three parallel links—the two shortlinks 1004L, 1004R and the tiller link 1001. However in practice, themanufacturing precision of the components is very good and the inherentcompliance of the assembled mechanism allows the pivotable parallelogrammechanism 1050 to function well without binding. Note that the groundpivot of the tiller link 1001 at axis 1303 is allowed to float on aseparate mounting plate during assembly and thus can find the optimalassembly location before being tightened down.

Referring now to FIG. 14, a bottom perspective view of a short link 1004is illustrated. FIG. 14 better illustrates the cam follower 1042attached near the end of each of the two short links 1004L,1004R. Eachcam follower 1042 engages the cam follower slot 1060L,1060R machinedinto the respective cam plates 1006L, 1006R. FIG. 14 better illustratesthe bearing 1441 inserted in the short link 1004 so the link can pivotabout the pivotal shaft 1041. FIG. 14 also illustrates a back side of apivotal shaft 1020 coupled to the short link 1004 where the long link1002 may be pivotally coupled.

Referring now to FIG. 15, a bottom cutaway perspective view of a portionof the steering mechanism of the PSC 152 is illustrated. FIG. 15 betterillustrates the cam followers 1042 of each short link 1004L,1004Rrespectively within the cam follower slots 1060L,1060R of the cam plates1006L,1006R. FIG. 15 further illustrates the meshing of the pinion gear908 of the tiller 202 with the gear sector 1010 of the tiller link 1001.

As the pivotable parallelogram mechanism 1050 moves back and forthdriven by the tiller 202, the cam followers 1042 drive the left camplate 1006L and the right cam plate 1006R in a unique way. Through thecombination of link lengths, pivot locations, and geometricrelationships, the motion of the cam plates 1006L,1006R creates the leftand right angular motions required to substantially generate Ackermanmotion to the steerable wheels 205L, 105R over the complete range ofturning radii, from infinite radius (straight running) to zero radius(pivoting about a point between the front wheels) in either left orright turn directions.

Referring now back to FIG. 13, the left cam plate 1006L pivots about thegrounded axes 1304 and the right cam plate 1006R pivots about thegrounded axis 1305. The left short link 1004L pivots about the groundedaxis 1301 and the right short link 1004R pivots about the grounded axis1302.

Reference is now made to FIGS. 16 and 17A-17C. FIG. 16 illustrates bothleft and right sides of the steering system and its linkage. FIGS.17A-17C illustrate the right side of the steering system and the how thecam follower and the steering linkage move as the tiller is turnedbetween right and left through center.

In FIG. 16, the pivot plates 1606L,1606R are illustrated coupled to thechassis 210. The pivotal shafts 1061, about which the cam plates1006L,1006R pivot, are coupled to the pivot plates 1606L,1606R. FIG. 16further illustrates how the short links 1004L,1004R are pivotallycoupled to the chassis (ground) 210 at the pivotal shafts 1041 and howthe tiller link 1001 is pivotally coupled to the chassis (ground) 210 atthe pivotal shaft 1013.

As discussed previously with reference to FIG. 11, the right sideparallelogram linkage 1100R includes the cam plate 1006R, a rearsteering link 1102R, a front steering link 1102F, and a caster link 1104pivotally coupled together at the pivotal shafts 1066,1067,1106,1107.The pivotal shafts form axes that are referenced using the samereference number for convenience.

In FIG. 17A, the steering system including the parallelogram linkage ispositioned as illustrated in a nominal, straight running direction. Thatis, the steering system is centered so that the steerable wheels arestraight and the mobile base 200 and PSC 152 moves in a straightdirection when driven by the motorized wheels forwards or backwards.Additionally, the tiller link 1001 is centered and pointing in astraight direction. The long link 1002 is parallel to the axes 302,303through the axles in the steerable wheels. The left and right shortlinks 1004L-1004R are centered and pointing in a straight direction suchthat cam plates 1006L,1006R are in a centered position.

In FIG. 17A with the right steerable wheel 205R point straight, it has aright wheel angle (RWA) of substantially zero degrees with reference toline 1700B.

The right side parallelogram linkage 1100R forms a parallelogram 1701 inFIGS. 17A-17C having a top side 1701T along the front steering link1102F between axes 1066,1106, a bottom side 1701B along the rearsteering link 1102R between axes 1067,1107, a left side 1701L along thecam plate 1006R between axes 1066,1067; and a right side 1701R along thecaster link 1104 between axes 1106,1107 as illustrated in FIG. 17A. Theleft side parallelogram linkage 1100L forms a mirror image of theparallelogram 1701 when viewed with the tiller centered having a tillerangle of zero degrees. The parallelogram linkage 1100 maintains theparallelism between sides of the parallelogram 1701 as the parallelogramshifts and the angles between the sides 1701T,1701L,1701B,1701R of theparallelogram 1701 changes.

At the axis 1061 of the pivotal shaft 1061 about which the cam plate1006R pivots, a fixed cam plate angle FCPA of ninety degrees is formedbetween lines out to each of the axis 1066 and 1067 along the arms orprongs of the letter-V-like shape of the cam plate. Similarly at theaxis 1210 of the pivotal shaft 1206 of the wheel assembly 1200 (see FIG.12), a fixed caster link angle FCLA of ninety degrees is formed betweenlines out to each of the axis 1106 and 1107 in the caster link 1104. Forthis reason, the parallelogram linkage may also be referred to assine/cosine parallelogram linkage since the equations underlying themechanical advantage computation of the linkage are sine and cosinewaves that are offset by a FCPA and FCLA of ninety degrees. When onelink's mechanical advantage is “going to zero”, the other link'smechanical advantage is “going to maximum”—a property of sine and cosinewaves

While the fixed cam plate angle and the fixed caster link angle FCLA areninety degrees in a preferred embodiment of the invention, other fixedangles between the arms of the cam plate and the arms of the caster linkmay be formed and diverge from an ideal Sine/Cosine parallelogramlinkage.

A cam plate angle CPA and a caster link angle CLA can be defined in thesteering linkage 1100R with reference to the lines 1700A-1700B in FIG.17A-17C, respectively. The cam plate angle CPA is formed at the axis1061 of the cam plate 1006R between a line extending between axis1061,1066 and the line 1700A. The caster link angle CLA is formed at theaxis 1210 of the wheel assembly 1200 between a line extending betweenaxis 1210,1106 and the line 1700B. The CPA and the CLA are made to beequivalent angles by the steering linkage 1100R and the parallelogram1701.

In FIG. 17A with the steering system centered, the CPA and CLA areapproximately thirty-four degrees each in one embodiment of theinvention.

In FIG. 17B, the steering system including the parallelogram linkage1100 is positioned as illustrated to make a minimum radius left turn.Additionally, the tiller link 1001 is pivoted to the right. The longlink 1002 is linearly shifted to the right from its centered position.The left and right short links 1004L-1004R are pivoted to the right fromtheir centered positions such that cam plates 1006L,1006R are pivotedabout their respective pivotal shafts 1061. The cam plate angle CPA andCLA are both approximately negative thirteen and one-half degrees in oneembodiment of the invention.

In FIG. 17C, the steering system including the parallelogram linkage1100 is positioned as illustrated to make a minimum radius right turn.Additionally, the tiller link 1001 is pivoted to the left. The long link1002 is linearly shifted to the left from its centered position. Theleft and right short links 1004L-1004R are pivoted to the left fromtheir centered positions such that cam plates 1006L,1006R are pivotedabout their respective pivotal shafts 1061. The cam plate angle CPA andCLA are approximately positive one-hundred twelve and two-tenths degreeseach in one embodiment of the invention.

Knowing the cam plate angle CPA with the vertical line 1700A (runningfrom front to back on the PSC) and the caster link angle CLA with thevertical line 1700B are approximately negative 13.5 degrees for making aminimum left turn as illustrated in FIG. 17B and approximately 112.2 formaking a right turn as illustrated in FIG. 17C, the right wheel angleRWA of the right steerable wheel 205R can be computed in each case.

Assuming the mobile base is moving forward and making a left turn withthe linkage position as shown in FIG. 17B, the right steerable wheel205R is the outer wheel along the turning radius. In one embodiment ofthe invention, the right steerable wheel 205R is moved to have a RWA ofapproximately negative forty-seven degrees (34 plus 13) with referenceto line 1700B.

Assuming the mobile base is moving forward and making a minimum rightturn with the linkage position as shown in FIG. 17B, the right steerablewheel 205R is the inner wheel along the turning radius and is to beturned more sharply. In one embodiment of the invention, the rightsteerable wheel 205R is moved to have a RWA of approximately positiveseventy-eight degrees (112 minus 34) with reference to line 1700B in oneembodiment of the invention.

Thus, in accordance with Ackerman steering principles, the PSC steeringsystem and linkage turns the inner steerable wheel more sharply than theouter steerable wheel when making tight radius turns.

Reference is now made to FIGS. 18A-18C showing schematic illustrationsof a parallelogram linkage 1800 and the application and transfer oftorque. Additionally, a fixed cam plate angle FCPA of ninety degrees anda fixed caster link angle FCLA of ninety degrees are illustrated inFIGS. 18A-18C between arms A and B. While the fixed cam plate angle andthe fixed caster link angle FCLA are ninety degrees in a preferredembodiment of the invention, other fixed angles between the arms of thecam plate and the arms of the caster link may be formed and diverge froman ideal Sine/Cosine parallelogram linkage.

In FIG. 18A, the parallelogram linkage 1800 is in a nominal position(e.g. arm A at forty-five degrees from vertical). Both of the arm pairsA-A and B-B are in a position to equally transmit torque from thepivotal shaft 1061 on the left to the pivotal shaft 1210 on the right(for example). The parallelogram linkage 1800 is coupled to chassisground at the pivotal shafts 1061,1210.

In FIG. 18B, the parallelogram linkage 1800 has experienced a clockwiseCW motion of forty-five degrees from the position illustrated in FIG.18A. The arm pair A-A is positioned so that it has a maximum mechanicaladvantage, while the arm pair B-B is positioned so that all of itsmechanical advantage is lost.

In FIG. 18C, the parallelogram linkage 1800 has experienced acounter-clockwise CCW motion of forty-five degrees from the positionillustrated in FIG. 18A. The arm pair A-A is positioned so that it haslost all of its mechanical advantage, while the arm pair B-B ispositioned so that it has a maximum mechanical advantage.

This illustrates that by using the parallelogram linkage disclosedherein that it is possible to transmit torque over a much larger rangeof motion than would be possible if only one arm pair (A-A or B-B) wereused. For practical purposes, a single arm pair version might work wellfor ninety degrees or one-hundred degrees of motion. However, theparallelogram linkage disclosed herein with both arm pairs (A-A and B-B)can transmit torque effectively for a full rotation of three hundredsixty degrees. In one embodiment of the invention, torque is transferredover a range of motion of one-hundred twenty-five degrees. Bymaintaining a mechanical advantage over a range of motions in theparallelogram linkage, the steering of heavy mobile medical equipmentcan be eased by reducing the torque required to turn the tiller and thesteerable wheels.

In FIG. 18A, there is an offset angle OA (previously referred to as camplate angle CPA) between the longitudinal line 1300A and arm A on theleft when the steering mechanism is centered. As this steering mechanismcan transmit torque over a full rotation (360 degrees) which is notrequired for implementation, the initial offset angle is essentially afree variable and was chosen for reasons of mechanical packaging andmechanical clearance.

The parallelogram steering linkage has been shown to work veryeffectively for steering the PSC 152. The embodiments of the steeringmechanism disclosed herein provides a small turning radius(theoretically down to a zero turning radius) (See FIG. 5). Theembodiments of the invention provide a dual steering axis to increasestability and ease the steering of heavy mobile medical equipment, suchas the PSC 152.

Alternate Steering Mechanism

FIGS. 7-17 illustrate a steering system between the steerable wheels205L,205R that employs rotary joints and parallelogram linkage toprovide a greater range of motion, a more compact size, and betteraesthetics. Instead of parallelogram linkage, a linear sliding bar and atiller cam arm may be employed.

Referring now to FIGS. 19 and 20A-20B, a steering system 1900 isillustrated. The steering system 1900 is an alternate embodiment of theinvention with elements above the steerable wheels 205L-205R. Thesteering system 1900 includes a pair of angled arms 1902L,1902R; asliding bar 1906; and a tiller link 1920 moveably coupled together asshown.

As shown in FIG. 19, each of the angled arms 1902L,1902R has a linearcam follower slot 1904. The left angled arm 1902L is coupled to the leftsteerable wheel 205L to pivot it about its axis 1210. The right angledarm 1902R is coupled to the right steerable wheel 205R to pivot it aboutits axis 1210.

The sliding bar 1906 has a pair of cam followers 1908 inserted into thepair of linear cam follower slots 1904 of the pair of angled arms1902L,1902R. The sliding bar may further have a cam follower 1910 forinsertion into a cam follower slot.

The tiller link 1920 has a linear cam follower slot 1922 over the camfollower 1910 in the sliding bar 1906. With respect to the chassis 210,the tiller link 1920 pivots about a pivot point 1924 near one end. Thetiller link 1920 may coupled to the tiller 202 in various ways.

In a straight steering position, as is shown in FIG. 19, each of thepair of angled arms has an offset angle 1930 that allows the sliding bar1906 to move a linear distance 1932 to pivot the steerable wheels. Thelinearly sliding bar 1906 actuates the pair of angled arms 1902L,1902Rby way of the cam follower 1908 sliding within the cam follower slot1904.

Referring now to FIGS. 20A-20B, the steering system 1900 may furtherhave a pair of ground links 2002L,2002R to assure the sliding bar 1906slides linearly. As show in FIGS. 20A-20B, each of the pair of groundlinks 2002L,2002R are spaced apart from each other. Near one end, eachof the pair of ground links are pivotally coupled near opposing ends ofthe sliding bar 1906 at the cam followers 1908. Near an opposite end,each of the pair of ground links are pivotally coupled to the chassis210 at spaced apart pivot points 2012

CONCLUSION

The embodiments of the invention are thus described. While embodimentsof the invention were described with reference to a patient side cart ofa robotic surgical system, the embodiments of the invention are not solimited as they are equally applicable to other heavy medical equipmentrequiring a steering system to move the equipment from one position toanother.

It is to be understood that the exemplary embodiments described andshown in the accompanying drawings are merely illustrative of and notrestrictive on the broad invention, and that the embodiments of theinvention not be limited to the specific constructions and arrangementsshown and described, since various other modifications may occur tothose ordinarily skilled in the art. Rather, the embodiments of theinvention should be construed according to the claims that follow below.

1. A method for steering mobile medical equipment having four wheels,the method comprising: supporting medical equipment with a base above afloor over which a left steerable wheel, a right steerable wheel, and apair of front wheels roll; receiving an input steering angle other thanzero; linearly sweeping a long link in response to the input steeringangle, pivoting a pair of short links in response to the linearlysweeping of the long link; pivoting a pair of cam plates in response tothe pivoting of the pair of short links; transferring the pivoting ofone of the pair of cam plates to a left wheel assembly to position theleft steerable wheel at a left wheel angle; and transferring thepivoting of another one of the pair of cam plates to a right wheelassembly to position the right steerable wheel at a right wheel angle.2. The method of claim 1, further comprising pivoting a tiller link toreceive the input steering angle.
 3. The method of claim 2, wherein thepair of front wheels are motorized wheels and the method furthercomprises: driving the pair of motorized wheels to move the mobilemedical equipment over the floor.
 4. The method of claim 1, wherein theposition of the right steerable wheel differs from the position of theleft steerable wheel such that an axis of rotation of the pair of frontwheels substantially intersects different axes of rotation of the rightsteerable wheel and the left steerable wheel at a center of turn to turnthe mobile medical equipment over the floor substantially around thecenter of turn.
 5. The method of claim 1, wherein the medical equipmentis a patient side cart of a robotic surgical system including one ormore robotic surgical arms.
 6. The method of claim 1, wherein the firstwheel angle of the first steerable wheel and the second wheel angle ofthe second steerable wheel are limited to provide a radius turn with aradius of not less than half a width of the base.
 7. A method forsteering mobile medical equipment having four wheels, the methodcomprising supporting medical equipment with a base above a floor overwhich a left steerable wheel, a right steerable wheel, and a pair offront motorized wheels roll; receiving an input steering angle otherthan zero; linearly sweeping a long link in response to the inputsteering angle, pivoting a pair of short links in response to thelinearly sweeping of the long link; pivoting a pair of cam plates inresponse to the pivoting of the pair of short links; positioning theleft steerable wheel with a left wheel assembly at a left wheel angle inresponse to the pivoting of one of the pair of cam plates; positioningthe right steerable wheel with a right wheel assembly at a right wheelangle in response to the pivoting of another one of the pair of camplates; and limiting the generating of the left wheel angle and theright wheel angle to avoid radius turns of substantially zero and avoiddriving a first motorized wheel of the pair of front motorized wheels inone direction of rotation while concurrently driving a second motorizedwheel of the pair of front motorized wheels in an opposite direction ofrotation.
 8. The method of claim 7, wherein the limiting of thegenerating of the left wheel angle and the right wheel angle includeskeeping the right steerable wheel and the left steerable wheel frompointing in opposite directions, wherein left and right are oppositedirections.
 9. The method of claim 8, wherein the limiting of thegenerating of the left wheel angle and the right wheel angle includeskeeping the right steerable wheel and the left steerable wheel pointingtowards a similar direction.
 10. The method of claim 9, wherein thesimilar direction is left and the right steerable wheel and the leftsteerable wheel are kept pointing towards the left to avoid radius turnsof substantially zero degrees.
 11. The method of claim 9, wherein thesimilar direction is right and the right steerable wheel and the leftsteerable wheel are kept pointing towards the right to avoid radiusturns of substantially zero degrees.
 12. The method of claim 7, whereinthe position of the right steerable wheel differs from the position ofthe left steerable wheel such that an axis of rotation of the pair offront wheels substantially intersects different axes of rotation of theright steerable wheel and the left steerable wheel at a center of turnto turn the mobile medical equipment over the floor substantially aroundthe center of turn.
 13. The method of claim 7, wherein the medicalequipment is a patient side cart of a robotic surgical system includingone or more robotic surgical arms.
 14. The method of claim 7, furthercomprising: the pair of motorized wheels are spaced apart from eachother.
 15. The method of claim 14, further comprising: driving a firstmotorized wheel of the pair of motorized wheels in a first direction ofrotation with a first motor.
 16. The method of claim 15, furthercomprising: driving a second motorized wheel of the pair of motorizedwheels in the first direction of rotation with a second motor; andwherein the first and second motors are spaced apart from each other.17. The method of claim 15, wherein the first and second motors arespaced apart from each other and the method further comprises: afterdriving the first motorized wheel, driving a second motorized wheel ofthe pair of motorized wheels in a second direction of rotation with asecond motor opposite the first direction.